Sikorsky S-92: From Design to Operations
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I don't think the REAL cause has been identified or at least I can find no reference to it.
Why did the titanium stud break in the first place? Over torquing during installation? Harmonic vibration? What are the pros and cons of steel over titanium and vise versa?
Why did the titanium stud break in the first place? Over torquing during installation? Harmonic vibration? What are the pros and cons of steel over titanium and vise versa?
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300 feet or 9000 feet....if you have a cast iron failure....you have pretty well had the schnitzel!
Regards,
AV8
Wiggins,
Drive yer Chevy off a 300 foot high cliff at 120 mph.....and tell me about the outcome!
Much the same as having a MGB come unstuck as you are whizzing about the sky in your trusty machine
Drive yer Chevy off a 300 foot high cliff at 120 mph.....and tell me about the outcome!
Much the same as having a MGB come unstuck as you are whizzing about the sky in your trusty machine
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Seems likely it was a significant link in the chain - the other links probably being that the aircraft should never have received certification against FAR29 in the first place, and the flawed information circulating about crew actions in the event of gearbox oil pressure loss
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MGB Design
How about making it a certification requirement that the MGB is dry-run-tested to identify the fail-point and to include in the basic architecture that this fail-point must not prevent the entry into safe autorotation.
Clearly lubrication of the upper casing mast bearing would be an issue but a 'bearing within a bearing' design with the outer (grease-packed) bearing pegged to the casing by shear pins. The inner (normal) bearing packs up under dry load and the shear pins break, leaving 'x' number of minutes of a grease-packed roller bearing to get you down.
G
Clearly lubrication of the upper casing mast bearing would be an issue but a 'bearing within a bearing' design with the outer (grease-packed) bearing pegged to the casing by shear pins. The inner (normal) bearing packs up under dry load and the shear pins break, leaving 'x' number of minutes of a grease-packed roller bearing to get you down.
G
Brian
The whole point of creating new certification standards is to raise the bar - give the manufaturers a bit of a challenge to move designs along.
So not really, other manufacturers manage it. Perhaps not by pure dry running - there is a massive amount of energy going through a transmission, losses cause lots of heat and a slight increase in friction and loss of cooling fluid will generate extremely high temperatures in the gears/bearings. High temperatures cause more friction and damage and you are likely to get rapid damage runaway. 30 mins is a long time!
But it can be done by other means - in the case of the EC225 its by a separate total-loss atomised glycol/air injection system whose primary function is cooling, secondary function a bit of lubrication. I'm not sure how the 139 does it nor how the 175 will do it, but they do/will
The 225 system is perhaps a little non-elegant - lots of pipes going into the gearbox, a system that is never operated except in emergency and can only be tested by engineering - but it does fully comply with 927.
But as I said, non-compliance with 927 was not the cause of the Cougar accident, only a link in the chain. If it had been a 225, they would have 30mins at Vy after total loss of oil pressure, that's 40nm in still air. I doubt that would have been enough to find somewhere dry to land, and the pilots would still have been faced with a need to ditch in a nasty-looking sea, they would just have had another 30 mins to think about it, wake up SAR etc.
HC
do you, or others, think perhaps the the requirements of 927, while admirable in intent, may just be a little ambitious given the task being asked of a MGB and the state of the art
So not really, other manufacturers manage it. Perhaps not by pure dry running - there is a massive amount of energy going through a transmission, losses cause lots of heat and a slight increase in friction and loss of cooling fluid will generate extremely high temperatures in the gears/bearings. High temperatures cause more friction and damage and you are likely to get rapid damage runaway. 30 mins is a long time!
But it can be done by other means - in the case of the EC225 its by a separate total-loss atomised glycol/air injection system whose primary function is cooling, secondary function a bit of lubrication. I'm not sure how the 139 does it nor how the 175 will do it, but they do/will
The 225 system is perhaps a little non-elegant - lots of pipes going into the gearbox, a system that is never operated except in emergency and can only be tested by engineering - but it does fully comply with 927.
But as I said, non-compliance with 927 was not the cause of the Cougar accident, only a link in the chain. If it had been a 225, they would have 30mins at Vy after total loss of oil pressure, that's 40nm in still air. I doubt that would have been enough to find somewhere dry to land, and the pilots would still have been faced with a need to ditch in a nasty-looking sea, they would just have had another 30 mins to think about it, wake up SAR etc.
HC
Last edited by HeliComparator; 22nd Mar 2009 at 09:22.
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Originally Posted by Walrus75
They got down to 800 feet and had time to spare, look here:
FlightAware > Live Flight Tracker > Track Log > CHI91 > 12-Mar-2009 > CYYT-CHIB
They had time to get down to the deck but if you look at the 3 minutes between 8:21 and 8:24 they must have hoped they were out of the woods (800 feet and speed back up to 133 Knots), which makes the last minute particularly sad reading. 10 minutes from incident occuring to being in the drink is particularly worrying.
FlightAware > Live Flight Tracker > Track Log > CHI91 > 12-Mar-2009 > CYYT-CHIB
They had time to get down to the deck but if you look at the 3 minutes between 8:21 and 8:24 they must have hoped they were out of the woods (800 feet and speed back up to 133 Knots), which makes the last minute particularly sad reading. 10 minutes from incident occuring to being in the drink is particularly worrying.
Walrus, I had not seen the flight track data. It really sheds different light on the possible cause. Very worrying.
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Advance in any safety endeavour regardless if led by industry or legislation will always meet with the usual resistance from the chaps that look after the money. The critical continued operation of a transmission even for a limited time after a failure of a lubrication system is one area that all those involved in flight operations have looked forward to over the years.
To say that it’s too difficult, cost implications are extreme or the technology that they are using is unable to comply is in my humble view feeble. To use holes in the legislation and smart legal interpretation to give an illusion of compliance is again in my view a travesty of the original intent.
In this case the gear box either conforms to the requirement or it douses not, if not then it is not in compliance, and the manufacture will need to put resources into making it compliant.
It would also seem that misinformation inferred that compliance was achieved.
I am not inferring that if it had been in compliance the outcome of the tragic event we all know about would have had a different outcome, we will never know, we will also never know what the actual decision process was that the crew used when reacting to the terrible sequence of events as they developed.
Safe flying to all.
Outhouse.
To say that it’s too difficult, cost implications are extreme or the technology that they are using is unable to comply is in my humble view feeble. To use holes in the legislation and smart legal interpretation to give an illusion of compliance is again in my view a travesty of the original intent.
In this case the gear box either conforms to the requirement or it douses not, if not then it is not in compliance, and the manufacture will need to put resources into making it compliant.
It would also seem that misinformation inferred that compliance was achieved.
I am not inferring that if it had been in compliance the outcome of the tragic event we all know about would have had a different outcome, we will never know, we will also never know what the actual decision process was that the crew used when reacting to the terrible sequence of events as they developed.
Safe flying to all.
Outhouse.
we will also never know what the actual decision process was that the crew used when reacting to the terrible sequence of events as they developed
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we will also never know what the actual decision process was that the crew used when reacting to the terrible sequence of events as they developed
I guess if one were designing from scratch, one might come up with this logic, or similar:
"as a leak progresses you would get the MP (main pump) caption when the feed pipe to the main pump became uncovered, temperature would go up (oil cooler automatically bypassed) and pressure would drop to a bar or so (14.7 psi), since the standby pump operates at lower pressure.
If the leak continued, the standby pump would eventually pump fresh air and the S/B P caption (standby pump) would illuminate, MGB Oil Pressure gauge would fall to zero and red MGB P central warning panel red light would come on, accompanied by an audio gong.
You would also expect oil temp to fall (no oil on sensor) and no chip lights (no oil circulating so no chips reaching the detectors.)
Oh - one manufacturer already thought of that
The RFM might highlight the last paragraph and it would be in the company EOPs, as the crew would most likely be quite aroused by the whole situation and could do with additional guidance.
What about adding external heat sensors to critical areas of the MGB,mast, and the like as a secondary system to the existing internal monitoring of lube oil?
Deux Cent Vignt Cinq - or you could just build a gearbox with an emergency lube system right from the start since they have been proven to work well. Then at that point where your post leaves the crew with no oil and no dry running, a decent gearbox with ELS would at least allow a controlled ditching.
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They are not grounded, but the January ASB has been revised to Revision A, that changes the compliance time from " at the next 1250 hour check or one year" to "before next flight." It also says "compliance is essential."
That's pretty clear guidance, which I think you'll find all operators are following
That's pretty clear guidance, which I think you'll find all operators are following
IMO the RFM should be updated to reflect land immediately on MGB lube oil pressure fail or < 5 psi and temperature increase above bearing design temperature until a new MGB design is available to provide an acceptable dry run time.
We'll soon know the full picture of what exactly happened once the TSB finish their initial investigation, until then I won't be traveling in a S-92a unless the pilot assures me that he'll land immediately on confirmed MGB lube oil failure.
Last edited by maxwelg2; 22nd Mar 2009 at 21:14.
Crab, I'm not familiar with the Sea King MGB - how does an emergency oil 'lube system' cope with a 'hole' in the MGB? Is it an entirely independant system, and does it not address pump failure rather than oil loss?
I understand the 225 MGB principle that HC describes, with a separate total loss cooling system.
I understand the 225 MGB principle that HC describes, with a separate total loss cooling system.
Outwest : I don't think the REAL cause has been identified or at least I can find no reference to it.
Why did the titanium stud break in the first place? Over torquing during installation? Harmonic vibration? What are the pros and cons of steel over titanium and vise versa?
Why did the titanium stud break in the first place? Over torquing during installation? Harmonic vibration? What are the pros and cons of steel over titanium and vise versa?
I think Outwest was onto something but the normally secretive Australians are being true to stereotype. What was the cause of the Broome incident stud failure? Did they break one or two studs? Did they fatigue slowly and progressively or snap without prior indications? Have any of the 600 or so titanium studs being removed now showing any sign of pending failure?
The MGB has a max oil pressure of only 130 psi, the three studs to hold the filter body on should be plenty for that. Probably even Canadian Tire bolts would be fine.
BTW, an AD may be out tomorrow calling for grounding until they are replaced. So far it is just the TSB (Canadian Transportation Safety Board) that has grounded Canadian S92. In the meantime some operators outside of Canadian jurisdiction are grounding their fleets, some aren't.
212man - the ELS uses the torquemeter pump which feeds from a lower sump in the MRGB than the normal pumps.
Unless the hole in the MRGB is right at the bottom then the ELS should provide lube (with no cooling) enough to get you home - at the very worst, it will allow you enough time to carry out a controlled ditching.
I think the Sea King MRGB has in the past explored most forms of failure and leak which is why the ELS was created - it is a shame that the same process has to be gone through with a modern helo
Unless the hole in the MRGB is right at the bottom then the ELS should provide lube (with no cooling) enough to get you home - at the very worst, it will allow you enough time to carry out a controlled ditching.
I think the Sea King MRGB has in the past explored most forms of failure and leak which is why the ELS was created - it is a shame that the same process has to be gone through with a modern helo
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212man - the ELS uses the torquemeter pump which feeds from a lower sump in the MRGB than the normal pumps.
Apache for HEMS - Strafe those Survivors!
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IIRC, and it has been several years since I last flew her, when they fitted the ELS to the Sea King they also changed the white metal bearings (which had the strength of cream cheese if not lubricated) to give a very minimal run-dry capability - 2.5 MINUTES. Basically if the ELS did not function you had enough time for a rapid descent to a controlled forced landing.
However, it has been a while and my memory may err on the details. What is shocking, if true, is that the S-92 does not have run-dry. I would have expected 30 minutes as a reasonable standard minimum on current generation aircraft.
Very, very sad
However, it has been a while and my memory may err on the details. What is shocking, if true, is that the S-92 does not have run-dry. I would have expected 30 minutes as a reasonable standard minimum on current generation aircraft.
Very, very sad
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So no dry run capability for the 61 / Seaking then, just technology in line with the age of the aircraft.
That actually got a belly laugh out of me HC, since the "New Technology" 225 uses a system that is very similar, although not as good in my opinion. The 61 ELS does actually have a published limit.....120 MINUTES !!!
